From: ccie2be (ccie2be@nyc.rr.com)
Date: Wed Jul 06 2005 - 13:50:42 GMT-3
Jerry,
Good going!!!
Your experiment proves that a requirement for mHSRP could be implied by
other configuration tasks.
I'm going to be taking the lab very soon and another question popped up in
my mind. I don't expect to see this but I also don't put anything beyond
Cisco to trick us up.
What do you think we should do if the lab directions prohibit us from adding
or changing ip addresses and we need to configure HRSP?
I don't think there's a way to config hsrp without adding an ip address.
While I'm aware of alternatives to HSRP such as VRRP and GLBP, I don't know
them well enough to know if any alternative to HSRP would satisfy these
constraints.
Any thoughts?
Thanks for trying this out and letting us know.
Tim
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
hulbertj@comcast.net
Sent: Wednesday, July 06, 2005 11:54 AM
To: ccie2be; 'Tom Lijnse'; 'Spyros Kranis'
Cc: ccielab@groupstudy.com
Subject: RE: 3550 port-security and HSRP.
I just labbed this real quick....it looks as if redirects works fine with
the standby use-bia command.
R1 R2 -----> R3-loopback
e0 e0
|----hsrp----|
R1 config:
interface Ethernet0/0
ip address 192.168.10.2 255.255.255.0
half-duplex
standby 1 ip 192.168.10.1
standby 1 priority 105
standby 1 preempt
R2 config:
interface Ethernet0/0
ip address 192.168.10.3 255.255.255.0
half-duplex
standby 1 ip 192.168.10.1
standby 1 preempt
Rack1R1#sho standby brief
P indicates configured to preempt. |
Interface Grp Prio P State Active Standby Virtual IP
Et0/0 1 105 P Active local 192.168.10.3 192.168.10.1
When a host on this segment tries to reach a destination reachable through
R2, this is what the debug on R1 show's;
Rack1R1#debug ip icmp
ICMP packet debugging is on
Rack1R1#
*Mar 4 17:31:29.385: ICMP: redirect not sent to 192.168.10.10 for dest
150.1.3.3
*Mar 4 17:31:29.385: ICMP: 192.168.10.3 does not contain an active HSRP
group
*Mar 4 17:31:30.383: ICMP: redirect not sent to 192.168.10.10 for dest
150.1.3.3
*Mar 4 17:31:30.387: ICMP: 192.168.10.3 does not contain an active HSRP
group
Rack1R1#
*Mar 4 17:31:32.386: ICMP: redirect not sent to 192.168.10.10 for dest
150.1.3.3
*Mar 4 17:31:32.386: ICMP: 192.168.10.3 does not contain an active HSRP
group
Added a second HSRP group to R1 & R2(Active):
R1
interface Ethernet0/0
ip address 192.168.10.2 255.255.255.0
half-duplex
standby use-bia
standby 1 ip 192.168.10.1
standby 1 priority 105
standby 1 preempt
standby 2 ip 192.168.10.254
standby 2 preempt
R2
interface Ethernet0/0
ip address 192.168.10.3 255.255.255.0
half-duplex
standby 1 ip 192.168.10.1
standby 1 preempt
standby 2 ip 192.168.10.254
standby 2 priority 105
standby 2 preempt
Now I can see this on R1's debug.
Rack1R1#
*Mar 4 17:38:13.111: ICMP: HSRP changing redirect sent to 192.168.10.10 for
dest 150.1.3.3
*Mar 4 17:38:13.111: ICMP: gw 192.168.10.3 -> 192.168.10.254, src
192.168.10.1
*Mar 4 17:38:13.111: ICMP: Use HSRP virtual address 192.168.10.1 as ICMP
src
*Mar 4 17:38:13.111: ICMP: redirect sent to 192.168.10.10 for dest
150.1.3.3, use gw 192.168.10.254
Rack1R1#sho standby
Ethernet0/0 - Group 1
State is Active
4 state changes, last state change 00:03:23
Virtual IP address is 192.168.10.1
Active virtual MAC address is 00b0.6405.3100
Local virtual MAC address is 00b0.6405.3100 (bia)
Hello time 3 sec, hold time 10 sec
Next hello sent in 0.657 secs
Preemption enabled
Active router is local
Standby router is 192.168.10.3, priority 100 (expires in 8.722 sec)
Priority 105 (configured 105)
IP redundancy name is "hsrp-Et0/0-1" (default)
Ethernet0/0 - Group 2
State is Standby
1 state change, last state change 00:00:18
Virtual IP address is 192.168.10.254
Active virtual MAC address is 0030.94bc.3320
Local virtual MAC address is 00b0.6405.3100 (bia)
Hello time 3 sec, hold time 10 sec
Next hello sent in 2.424 secs
Preemption enabled
Active router is 192.168.10.3, priority 105 (expires in 7.007 sec)
Standby router is local
Priority 100 (default 100)
-------------- Original message --------------
> One more thing to think about. With the below statement from the link Tom
> provided (thanks):
>
> "In certain configurations, such as the use of the standby use-bia
interface
> configuration command specified on an interface, redirects cannot be sent.
In
> this case, the HSRP groups use the interface MAC address as their virtual
MAC
> address. The router now cannot determine if the default gateway of the
host is
> the real IP address or one of the HSRP virtual IP addresses that are
active on
> the interface."
>
> I would take this as meaning, that if I wanted optimal operation, I would
not
> implement 'standby use-bia', and I would have to rethink my port-security
> configuration. Does anyone agree or disagree?
>
> I will try to lab this up later today.
>
> Thanks,
> Jerry
>
> -------------- Original message --------------
>
> > Hi Tom,
> >
> > Thanks again for your response.
> >
> > I read the link you sent me and see I was wrong on at least one point.
> >
> > Per this link, "When running HSRP, it is important to prevent hosts from
> > discovering the interface (or real) MAC addresses of routers in the HSRP
> > group. If a host is redirected by ICMP to the real MAC address of a
router,
> > and that router later fails, then packets from the host will be lost."
> >
> > But, given the above, how could a packet get to net 3 if R1 is the
active
> > router and R1 and R2 are in the same group?
> >
> > R1 R2 -----> R3 net3
> > e0 e0
> > |----hsrp----|
> > |
> > other hosts
> >
> > It seems to me that this isn't possible. To solve this problem it seems
> > that 2 groups must be configured and R2 must be the active router for
the
> > other group. This way for hosts that use R1 as their default gateway
will
> > be redirected to the virtual mac address of the other group.
> >
> > Am I on the right track now?
> >
> > TIA, Tim
> >
> > -----Original Message-----
> > From: Tom Lijnse [mailto:Tom.Lijnse@globalknowledge.nl]
> > Sent: Wednesday, July 06, 2005 9:18 AM
> > To: ccie2be; Spyros Kranis
> > Cc: ccielab@groupstudy.com
> > Subject: RE: 3550 port-security and HSRP.
> >
> > Hi Tim,
> >
> > Okay, let's see if I can answer your questions:
> >
> > - "When HSRP is configured this way with the use-bia command, is the
> > failover fast enough that any active sessions that hosts might have at
> > the time of switch over remain intact?"
> >
> > As far as I know 'use-bia' has similar convergence to normal HSRP. The
> > only extra step is that when the Standby becomes Active it has to send
> > out the gratuitous arp-replies and the hosts need to update their
> > arp-caches, but as far as I can see that should only add milliseconds to
> > the convergence time. I haven't tested very extensively, but when I did
> > use it, it never seemed slower than normal HSRP.
> >
> > - "I'm wondering if it's possible to config port security on the 3550
> > and the use-bia on the routers such that a failover is transparent to
> > hosts sessions maybe by lowering hsrp timers?"
> >
> > As far as I can see this comes down to the same issue. (This depends on
> > what you mean by transparent). Convergence time for HSRP is determined
> > by the time it takes for the Standby to discover that the Active Router
> > disappeared, so this is mainly determined by the hello and holdtime.
> > Setting these to lower values will decrease the convergence time.
> > Whether or not you're using 'use-bia' seems negligible to me.
> >
> > - " Suppose your topology was like this:
> >
> >
> > R1 R2 -----> R3 net3
> > e0 e0
> > |----hsrp----|
> > |
> > other hosts
> >
> >
> > R1 is the active router. R2 is the standby router but packets must get
> > to
> > R3 to get to net3.
> >
> > How should HSRP be configured such that the hosts use R1 for all
> > destinations except for net3?"
> >
> > The whole story about ICMP unreachables being disabled when you enable
> > HSRP isn't entirely true anymore. You may want to read the following bit
> > on the Doc-CD:
> >
> > http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/
> > fipr_c/ipcprt1/1cfip.htm#wp1044507
> >
> > After reading this and possibly quickly labbing it up I think you should
> > be able to come up with an answer to your own question. In the end I
> > think this would be more educational than me just giving you the answer,
> > but let me know when you need a hint.
> >
> > Regards,
> >
> > Tom Lijnse
> >
> > CCIE #11031
> > Global Knowledge
> >
> > _______________________________________________________________________
> > Subscription information may be found at:
> > http://www.groupstudy.com/list/CCIELab.html
>
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